1. Field of the Invention
This invention relates generally to a sleeve-type flexible coupling for transmitting power between rotating shafts, more particularly to a sleeve-type flexible coupling having pronged, interlocking hubs, and specifically to a pronged coupling having a reinforced elastomeric sleeve with teeth that mesh with gaps between and grooves residing on loosely interlocking prongs.
2. Description of the Prior Art
Transferring power or rotational motion through flexible, elastomeric, sleeve-type, shaft couplings of various kinds is known. Examples of the kind of coupling design that relies on the shear strength of the sleeve are U.S. Pat. No. 6,283,868 and U.S. Pat. No. 6,142,878. Shear-type sleeve couplings generally have a pair of opposing hubs or end pieces adapted to attach to two coaxial shafts, and a connecting sleeve extending between and engaging the two hubs. The hubs and sleeves engage via a plurality of axially extending ribs or teeth along at least a portion of the inner periphery of the sleeve for meshing with grooves in oppositely disposed end pieces to form a flexible coupling assembly. These couplings generally provide some vibration isolation and accommodate some shaft misalignment.
Problems with these flexible sleeve couplings include that elastomer teeth can shear off under a torsional load, the sleeve itself can shear into two pieces in the area intermediate between the two engaged ends, and the sleeve can expand or explode at high speed from centrifugal force. Methods to improve tooth shear resistance include reinforcing the elastomer of the sleeve with chopped or continuous fibers, using higher strength plastics, composites or elastomers, or reinforcing the teeth with fabric. Methods to protect the sleeve from centrifugal forces include reinforcing the sleeve with tensile cords, providing the hubs with an annular cavity into which the sleeve engages as disclosed in U.S. Pat. No. 5,660,591 and providing an external metal band as disclosed in U.S. Pat. No. 3,362,191. Methods to prevent the sleeve from twisting and or shearing between the hubs include using one inner male hub and one outer female hub with the annular sleeve engaged there between as disclosed in U.S. Pat. No. 4,357,137, thickening the intermediate region of the sleeve as disclosed in U.S. Pat. No. 6,671,475, or using hubs with radially overlapping teeth or prongs as disclosed in U.S. Pat. No. 5,295,911. Typical commercial sleeves are thus relatively thick and bulky. These shear-type coupling designs provide machinery protection by failure of the elastomer sleeve under excessive torque, although sometimes fail-safe operation is more desirable.
One fail-safe design uses hubs which have circumferentially overlapping teeth or prongs with large gaps between the teeth into which gaps an elastomeric element is inserted. During operation, the elastomeric element resides in compression between driver and driven teeth, so high loads are possible. If the elastomer fails, the overlapped teeth continue to drive the load. Another method to provide fail-safe transmission of power on failure of the elastomer is to provide a rigid engaging element which may be metal coated with elastomer as disclosed in U.S. Pat. No. 5,660,591. Because the elastomer layer is so thin, this fail-safe coupling provides very little flexibility and very little vibration isolation.
A pronged coupling having a flexible sleeve with internal teeth has been proposed in U.S. Pat. No. 3,360,962 and Japanese Unexamined Patent Publication 07-259876A. Each prong has a series of grooves which mesh with the teeth in the sleeve. During operation the elastomeric element resides in tension between a driver and a driven prong. Fail-safe operation is provided in the event of sleeve failure. While various embodiments are suggested, it is not known or taught how to combine the advantages of tension-type operation with the advantages of compression-type operation to achieve increased durability, increased torque rating, and/or decreased coupling size with less material usage.
Thus, the prior art fails to disclose a pronged coupling having a reinforced elastomeric sleeve with teeth that mesh with gaps between and grooves on interlocking prongs. The prior art fails to disclose a coupling sleeve with a dual-tooth profile.